Field
This disclosure relates generally to semiconductor devices, and more specifically, to recovering voltage beyond device voltage limits.
Related Art
Devices that operate in ultra-low power modes can be subjected to a high amount of back bias and sometimes voltages greater than oxides in the devices are designed to handle. For example, a back bias of −3 Volts may be required on a 0.9 Volt core device in a silicon on insulator (SOI) technology. In some thin film memory designs, as another example, a 14 Volt supply is required during erase even though oxide in the devices can only handle 9 volts. During a brown-out, it is desirable to recover bias voltages quickly to avoid damaging the devices. Recovering nodes with relatively large capacitance (e.g. nanoFarad) at these levels relatively quickly can pose a problem yet are required for fast wakeup, especially when the voltages being used are beyond the technology limits of the device. The voltages need to be recovered relatively fast especially in cases of brown out in which there is a race against power supply discharging in a matter of microseconds. Ultra-low power parts typically spend very little time in run mode after a deep sleep power down mode to minimize duty cycle. Accordingly, care must be taken in applying and recovering voltages applied to the devices.